Cordless telephone instruments for use in the home are widely available. Such systems, comprise a base unit and a remote handunit. The base unit is coupled to the telephone line and communicates with the remote handunit via FM radio signals. With such a cordless telephone system a user can remove the handunit from its cradle and carry it with him a short distance from his house yet still be able to make and receive telephone calls. Such a cordless telephone set is known from GE cordless telephone model number 2-9675 manufactured by Thomson Consumer Electronics, Inc. Indianapolis, Ind.
If the user is engaged in a conversation via a cordless telephone, and a third person within the user's house wishes to join in the telephone conversation, that person can simply pick up a "hard-wired" extension telephone. Unfortunately, the third person cannot maintain participation in the conversation without remaining in the immediate area of the hard-wired telephone unit.
A copending patent application bearing attorney docket number RCA 86,682 discloses a cordless telephone system which comprises a base unit and two handunits. In that system, a base unit transmits simultaneously to both handunits via two transmitter channels coupled to the same antenna, but during development of that system it was discovered that phase-locked loop (PLL) up-conversion used in the above-mentioned GE cordless telephone model number 2-9675 caused unacceptable intermodulation distortion in the transmitter signal from the base unit when the outputs of the transmitters were coupled together.